"It is a myth that rape is an inevitable part of conflict," the 39-year-old actress, wearing a crisp white Michael Kors skirt and blazer and her long hair tucked into a bun, told the crowd. "There is nothing inevitable about it. It is a weapon of war aimed at civilians. It has nothing to do with sex – everything to do with power. It is done to torture and humiliate innocent people and often very young children."

With 100 countries sending representatives to the summit – including the United States and all the G7 nations – as well as more than 900 experts participating, Jolie previously told PEOPLE that it is "the largest summit of its kind on this issue. There’s so many aspects to people wanting to change the world, and people come at it from different ways."

The four-day event is open to the public and features 200 events, including movie screenings (Jolie's In the Land of Blood and Honey screens Wednesday), panel discussions, an international marketplace and actors reading victim accounts.

'I Love Working in the Field'

Jolie isn't alone in the U.K. Fiancé Brad Pitt and their kids joined her, as they have on many of her humanitarian trips through the years. "I’ve worked for 12 years with the UN and I love working in the field," she told PEOPLE last month.

This summit, she says, is the culmination of the dozens of trips she's taken to war zones, where she has spoken to rape survivors. "Angelina has been working day and night on this," says Arminka Helic, senior adviser to Secretary Hague. "She's attended conferences, taken trips with us, has worked very hard on this."

One goal, Helic says, is to establish an international protocol for documenting and investigating sexual violence in war zones. Once adopted by each nation, international criminal courts can more effectively prosecute offenders, lessening the stigma suffered by victims.

During her speech, Jolie described the horrors she has witnessed during her travels to war-torn nations.

"I have met survivors from Afghanistan to Somalia, and they are just like us – with one crucial difference: We live in safe countries with doctors we can go to when we're hurt, police we can turn to when we're wronged and institutions that protect us," she told the crowd.

"They live in refugee camps or bombed-out streets in areas where there is no law, no protection and not even the hope of justice. And as an international community we are responsible for that."